This invention relates to both a method and an apparatus for separating and measuring solids from a multi-phase stream of well fluids.
When drilling a well or borehole into the earth and through underground formations a common concern in virtually every application is the collection, separation, disposal, and in some cases the measurement, of the well fluids expelled from the well during the drilling process. Regardless of whether an overbalanced, balanced or under balanced drilling technique is utilized, pressurized drilling fluid returns are expelled from the well and must be treated in order to separate the components, recycle particular materials, and process or otherwise dispose of the remaining fluids and their constituent parts. Depending upon the nature of the drilling process being utilized and the geology through which the wellbore is drilled, the drilling fluid returns may include a wide variety of solid, liquid and/or gas components. Where the well is an oil or gas well, drilling fluid returns typically include oil, water, rock particulants (sand), natural gas, and various other hydrocarbon compounds. The encountering of high pressure underground formations, in combination with the fact that in most drilling operations high pressure drilling fluids are pumped from the surface down into the borehole to help fluidize cuttings and drive them upwardly out of the well, results in the drilling fluid returns extracted from a well often being at a relatively high pressure. For environmental and economic reasons the multi-phase returns must usually be separated and processed before their components can be recycled and put to further use or disposed. Since the returns are in many cases at elevated pressures or contain noxious or hazardous materials, their processing necessitates the use of dedicated and specialized equipment.
Multi-phase well fluids are also typically generated during the fracing and testing of oil and gas wells, and are commonly encountered in producing wells. As in the case of the drilling of a wellbore into the earth, multi-phase returns generated in producing oil and gas wells, and those generated during the fracing or testing of a well, are typically processed with specialized equipment to separate their component parts, avoid the release of hazardous materials into the air or the environment, and in some cases to measure the volumetric rate of production of solid phase returns.
Current techniques and equipment that have been developed to process multi-phase well fluids typically employ the use of one or more separation vessels that are primarily designed to separate the solid, liquid and gas components of the returns. In some instances the treatment of the returns is carried out in two or more separate and distinct stages. For example, an initial separator may be utilized wherein a portion of the solid component (ie sand) is separated from the well returns. The gas, liquid and any solids that may be carried over into the gas and liquid phases are then transported to a subsequent separation stage for further processing. When a high pressure separator is used a significant amount of the sand is removed thereby helping to minimize erosional effects that may otherwise occur if the solid particulate material were allowed to flow through the piping, valves and other components of the separation system. In addition, since the sand is separated at full wellhead pressure, the relative size of the equipment necessary can be kept to a minimum as the process is conducted prior to any gas expansion that will occur at a downstream low pressure stage.
While such prior existing separation methods and devices have been relatively effective, they all suffer similar inherent limitations when it comes to the disposal or removal of sand separated out of the returns. Prior systems also do not readily provide for the volumetric measurement of the sand component expelled from the well. Traditionally sand that has been extracted from multi-phase well fluids by means of a separation vessel has been removed from the vessel through the manual operation of a dump valve or similar apparatus. As sand accumulates within the separation vessel an operator would typically activate a dump valve to allow the sand to be removed for further processing or disposal. In order to lengthen the interval between the time that an individual would be required to dump the accumulated sand, others have increased the size of their separation vessels providing a greater volume within which sand can accumulate. However, doing so runs contrary to one of the reasons for utilizing an initial well-head pressure separation stage; namely, the ability to minimize the size of the necessary equipment. As a result, others have suggested that the dump valve be controlled by a timer that is set to open the valve after a pre-determined interval. In such instances a xe2x80x9cguesstimatexe2x80x9d of the volume of solids produced over time is prepared and the timer controlling the dump valve set to correspond to an anticipated solid production level. Unfortunately, this less than scientific method creates significant problems when the valve is open for too long and gas carry under occurs (particularly if there is hydrogen sulfide present). Similarly, problems will be encountered where there are no solids present that require the opening of the dump valve, in which case there will be an unrestricted passage of multi-phase well fluids through the dump valve resulting in increased disposal costs. Further, where the time interval that the dump valve is left open is too short, an excessive amount of solids may build up within the separation vessel, potentially resulting in a solid carry over into the separation stage. An increased volume of solids in a subsequent separation stage can significantly increase the erosion of downstream piping and components.
The xe2x80x9ctimedxe2x80x9d method of opening and closing a dump valve suffers from the further limitation of making it difficult to measure the volume of solids produced from the well. To determine a solids production rate a separate tank (having some form of gauge or other measurement device) into which the solids can be placed and thereafter measured is most often used. Aside from having a low degree of accuracy, the use of such equipment increases the overall physical size of the separation system. If the well contains hydrogen sulfide or other toxic gases, it will be necessary to utilize a vacuum truck to remove the solids from the separation vessel thereby even further increasing the difficulty in measuring the volume of solids produced. As a result, such prior existing methods provide only a general estimate of the volume of solids production, at best.
Rather than directly measuring solids production, others have suggested monitoring for the presence of solids within multi-phase well fluid returns through the use of an erosion/corrosion probe. Such a unit is typically placed in a fitting within the returns line so that it intrudes into the stream of untreated well fluids flowing from the well to the separation system. The probe will then be exposed to the erosion generated by solids passing through the pipeline. A small voltage is passed through the probe such that as the probe erodes there is a reduction in its resistance that may be measured and used to calculate an equivalent reduction in probe diameter, and hence determine the presence of solids in the well returns. Unfortunately while such systems can be used to predict the presence of solids within well fluids, and to some degree an increase or decrease in the amount of solids present, they are incapable of quantifying the volume of solid production from the well. Other similar systems that are based upon acoustic probes generally only identify the presence of solids and their range of accuracy is normally limited at low solid concentrations.
The invention therefore provides a method and an apparatus for separating and measuring solids from multi-phase well fluids that helps to address some of the deficiencies in prior existing devices. The invention provides for the treatment of multi-phase well returns that allows for the automatic removal of accumulative solids from the separation vessel only when necessary, and then only to the extent that the solids are removed without the threat of gas or liquid carry under. At the same time, the invention provides a method and apparatus to accurately quantify the volume of solids that are produced by the well and separated from the well fluids.
Accordingly, in one of its aspects the invention provides a method for separating and measuring solids from multi-phase well fluids extracted from a well, the method comprising the steps of directing said multi-phase well fluids to a separator to separate at least a portion of any solids present in said well fluids from any liquid and gas phase components of said well fluid; establishing an upper maximum and a lower minimum limit within said separator for accumulated solids separated from said multi-phase well fluids, said upper maximum and lower minimum limits established through the use of at least one upper sensor and at least one lower sensor; upon said accumulated solids in said separator reaching said upper maximum limit, generating a first signal with said upper sensor and directing said first signal to a control module; upon said accumulated solids in said separator reaching said lower minimum limit, generating a second signal with said lower sensor and directing said second signal to said control module; and, upon receipt of said first signal said control module causing a dump valve operatively connected to said separator to open allowing a portion of said accumulated solids to be removed from said separator, upon receipt of said second signal said control module causing said dump valve to close and prevent further removal of accumulated solids from said separator to thereby limit liquid or gas carry under where said multi-phase well fluids include a liquid or gas component.
In a further aspect the invention provides a method for separating and measuring solids from multi-phase well fluids from a wellbore, the method comprising the steps of; directing multi-phase well fluids generated from the wellbore to a separator designed to separate at least a portion of any solids from gas phase components present in said multi-phase well fluids; through the use of at least one upper level sensor connected to said separator, establishing an upper maximum limit within said separator for the accumulation of solids separated from said multi-phase well fluids; through the use of at least one lower level sensor connected to said separator, establishing a lower minimum limit within said separator for accumulated solids separated from said multi-phase well fluid, said lower minimum limit designed to maintain a minimum volume of solids within said separator and to thereby help prevent gas carry under when solids are extracted from said separator; generating a first signal with said upper level sensor when the upper level of said accumulated solids in said separator reaches said upper maximum limit and generating a second signal with said lower level sensor when the upper level of said accumulated solids in said separator reaches said lower minimum limit, said first and second signals directed to a control module, said control module operating a dump valve connected to said separator and causing said dump valve to open and close to thereby maintain the level of said accumulated solids in said separator between said upper maximum and said lower minimum limits; and, with a density measuring device and a flow measurement device, measuring the density of solids separated from said multi-phase well fluids and calculating the flow of solids from said separator when said dump valve is open, thereafter, with said measured density and said calculated flow rate determining a volumetric measurement of solids separated from said multi-phase well fluids by said separator.
The invention also provides an apparatus for separating and measuring solids from multi-phase well fluids from a wellbore, the apparatus comprising; as separator for separating at least a portion of any solids from gas phase components present in said multi-phase well fluids; an upper solids level sensor connected to said separator, said upper solids level sensor generating a first signal when the upper level of accumulated solids within said separator reaches a pre-determined upper maximum level; a lower solids level sensor connected to said separator, said lower solids level sensor generating a second signal when the upper level of accumulated solids within said separator reaches a pre-determined lower minimum level; a dump valve operatively connected to said separator, said dump valve having an open and a closed position; and, a control module operatively connected to said dump valve to move said dump valve between said open and said closed positions, said control module receiving said first and second generated signals such that upon receipt of said first signal said control module causes said dump valve to move to said open position and upon receipt of said second signal said control module causes said dump valve to move to said closed position.
Further aspects and advantages of the invention will become apparent from the following description taken together with the accompanying drawings.